Advanced statistical analyses to reduce inconsistencies in bond strength data focused on donor factors: A six-factor analysis using linear mixed and nonlinear regression models.

PURPOSE: This study aimed to investigate the effects of the age and sex of tooth donors on dentin bond strength. METHODS: A total of 38 extracted teeth (12 male and 26 female donors; age range: 17-82 years) were used in this study. In addition to donor age and sex, four other microtensile bond strength (µTBS) test specimen factors were evaluated: dentin position, bonding area, presence of voids at the interface, and computed tomography (CT) values of dentin. The µTBS was measured immediately (24 h) and 6 months after storage in water. After the µTBS testing, linear mixed and nonlinear regression models were used to analyze the effects of these factors on the µTBS data. RESULTS: The results from the linear mixed model revealed that the bonding area (P = 0.02), presence of voids at the interface (P = 0.04), and storage time (P < 0.001) significantly affected bond strength. In contrast, no correlation was observed between the µ TBS and dentin position (P = 0.08) or sex (P = 0.07). The results of the nonlinear regression model with robust variance-covariance estimators revealed that age significantly affected bond strength (P < 0.001). In addition, a significant positive correlation was found between µTBS and age (P < 0.001), with nonlinearity (P = 0.002). However, no correlation was observed between the µTBS and CT values (P = 0.69) without nonlinearity (P = 0.39). CONCLUSIONS: These findings suggest that bond strength increases with age until 60 years but not afterward.

Effect of filler contents on the bond strength of CAD/CAM resin crowns: New resin primer versus conventional silane agents.

PURPOSE: This study aims to evaluate the effects of resin primers containing methyl methacrylate (MMA) and silane agent on the bonding effectiveness of indirect resin composite blocks with three different filler contents. METHODS: A commercially available computer-aided design/computer-aided manufacturing (CAD/CAM) resin composite block and two experimental resin composite blocks with different filler contents were alumina-blasted and two surface treatments (primer and silane agent) were applied. The resin cement was built up, and the micro-tensile bond strength (µTBS) was measured after 24 hours, 1 month or 3 months of water storage (n = 24 per group). The fracture surfaces after µTBS measurements and resin block/cement interface were observed by scanning electron microscopy (SEM). RESULTS: The primer treatment group showed a significantly higher bond strength than the silane group only in F0 (filler content 0 wt%) group (P < 0.001). In the primer group, F0 and F41 (filler content 41 wt%) groups showed significantly higher bond strengths than F82 (filler content 82 wt%) group (P < 0.001). In contrast, in the silane group, F41 group showed significantly higher bond strength than F0 and F82 groups (P < 0.001), and F82 group showed significantly higher bond strength than F0 group (P < 0.001). SEM revealed that the matrix resin was partially destroyed on the fracture surface of the primer group, and an uneven interface surface was observed compared with that of the silane group. CONCLUSIONS: MMA-containing primers showed higher bonding effectiveness to CAD/CAM resin composite blocks than the silane treatment.